The present invention relates generally to an apparatus for measuring parameters required for mounting opthalamic lenses in a spectacle frame and more specifically to measuring pupillary height with respect to the bottom edge or lower eye wire of the spectacle frame.
In order to determine the pupillary height for placement of progressive addition lenses, a standard rule or scale has been typically used to estimate the height of the center of the pupil with respect to the lowest part of the lower eye wire of the spectacle frame so that the measurements can be conveyed to the lens maker. However, in such manual ruler techniques, inaccuracy can be easily introduced resulting in patient dissatisfaction.
An example of such a known ruler-type gauge is disclosed in U.S. Pat. No. 3,987,554 issued on Oct. 26, 1976 to J. Pastore. The known gauge is inserted into the bevel (lens well) of the lower eye wire of the spectacle frame at its lowest part and by reading the graduation where an imaginary horizontal line passing through the center of the pupil would intersect the gauge, the pupillary height is estimated. However, the device is inconvenient to use and is prone to measurement errors caused by the following factors: 1) the patient's eyes would wander; 2) the optician approximates the center of the corneas or pupil by observation; 3) the optician approximates the imaginary line; 4) the optician approximates the lowest portion of the lower eye wire; and 5) proximity between patient and optician could cause eye strain to both the patient and the optician.
Other devices exist which include an ocular or eye-piece through which the optician observes the eye of the patient. The eye-piece typically includes a cross-hair or horizontal line which is aligned with the center of the eye. An example of such a known ocular positioning apparatus is disclosed in U.S. Pat. No. 5,167,074 issued on Dec. 1, 1992 to M. Weiss. The device provides a chin rest for maintaining the stability of the patient's head. The optician observes the center of the eye or other reference points on the patient's face through an ocular and moves the ocular along a vertical axis until the cross-hairs of the ocular are aligned with the appropriate reference point. The vertical distance traveled by the ocular represents the pupillary height of the patient. However, such a known device is extremely cumbersome and requires placement on a suitable table top and is preferably, permanently mounted to the table top. A significant drawback of this known device is that the cross-hairs of the optician's eye-piece are disposed relatively far away from the patient's eye. When the optician attempts to align the cross-hairs with the eye, the measurement of the distance, or the vertical distance that the eye-piece is displaced, depends upon the angle through which the optician views the patient's eye each time. This may result in a significant parallax error. During each attempt to align the cross-hairs with the eye, the optician must look through the exact center of the eye-piece to avoid introduction of such parallax errors. Such a task is difficult to accurately perform and often results in measurement errors.
Accordingly, it is an object of the present invention to substantially overcome the above-described problems.
It is another object of the present invention to provide a pupillary height meter which substantially eliminates parallax error.
It is a further object of the present invention to provide a pupillary height meter which measures the vertical distance from the bottom of the spectacle frame to the center of the cornea.
It is also an object of the present invention to provide a pupillary height meter which independently measures the pupillary height of each eye.
It is still an object of the present invention to provide a pupillary height meter that is physically compact and is easy to operate.